<!DOCTYPE html>
<html>

<head>
	<meta charset="UTF-8">
	<title>Bootstrap 实例</title>

	<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.0.0-beta/css/bootstrap.min.css" integrity="sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M"
	 crossorigin="anonymous">
	<style>
		img {
			max-width: 100%;
		}
	</style>
</head>

<body>
	<img
	srcset="img/256px.jpg 256w, img/512px.jpg 512w, img/720px.jpg 720w"
	sizes="(min-width: 720px) 720px, (min-width: 512px) 512px, 256px">

	<p>srcset：设置响应式 替换的图片</p>
	<p>sizes：设置响应式 图片的大小</p>
	<p>
		<b>缺点</b>：srcset的换图功能不兼容，只有火狐Firefox浏览器可用</p>
</body>

</html>